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Tuesday, October 09, 2007

Occasionally proponents of renewed DDT use will claim that the pesticide, banned in the United States as an ecological hazard, has no harmful effect on humans. That is actually not true, as there is already evidence of a connection with reproductive problems. In addition to early miscarriages, it may also cause premature birth or decrease men's sperm quality.

The results are something of a surprise, researchers said, because several previous studies have found no link between cancer and the insecticide, which was widely used during the 1950s and '60s but was banned in the United States in 1972.

The new work differs from all other studies, however, by focusing on the age at which women were exposed. Echoing the situation with some other breast cancer risks, such as radiation, it finds that DDT increases the risk of breast cancer in adulthood only if the exposure occurred at a young age, before the breasts were fully developed.

All told, girls who had the highest levels of the chemical in their blood during that crucial developmental period were five times more likely to get breast cancer years later than were girls who had the lowest levels. That fivefold increase is a bigger boost in risk than is now attributed to hormone replacement therapy or having a close relative with breast cancer.

It is too late for the study to be of much benefit to women who were exposed in this country. However, it ought to give pause to attempts to restart or expand its usage elsewhere. A pesticide that has long been known to have deleterious ecological effects and that may be harmful to humans should not be the first choice if better options are available.